Sex determination of Kelp Gull Larus dominicanus vetula using head and bill measurements

Abstract

Kelp Gulls Larus dominicanus are not sexually dimorphic by plumage or visual characteristics and it is therefore difficult to distinguish males from females in the field. This paper assesses the sexual size dimorphism in this species and provides reliable methods for predicting sex of measured individuals. Discriminant function analysis of three commonly measured morphometric characters of adult birds indicated that the combination of head length and bill depth were the most accurate variables to use in a discriminant function model, predicting the sex with 97% accuracy.